Captive panel fasteners are commonly used in applications where it is desirable to permanently attach one or more fasteners to a work piece, such as a panel that may be repeatedly removed and replaced. An example of such an application is in aircraft, where panels are routinely removed for aircraft inspection and/or maintenance and then reinstalled. In such situations, it is desirable to retain the fasteners with the panel, both to facilitate rapid re-installation of the panel and to prevent small parts, such as bolts and washers, from getting lost inside the airframe of the craft and potentially causing damage if they contact moving parts of the aircraft.
An example of a captive panel fastener 10 is shown in FIG. 1 and described in U.S. Pat. No. 4,655,658 to Bulent Gulistan, issued on Apr. 7, 1987. The fastener 10 has a head 12, a threaded shank 14, and an end 22 with an axial bore 20 extending partially through the shank 14. The shank 14 has two or more grooves 16 cut through the threads, and a washer 24 is positioned around shank 14 and has radially inwardly extending prongs 26 that are slideable within the grooves 16. The shank end 22 has a flange 18 that can be deformed, shown as 18-1 in dashed lines, to provide a stop that prevents the washer 24 from sliding off of the shank. The panel fastener can be mounted onto a panel by passing the shank 14 through a hole in the panel, placing the pronged washer 24 onto the threaded shank 14, and then deforming the flange 18 to retain the washer on the shank, with the panel between the fastener head 12 and the washer 24.
The Gulistan U.S. Pat. No. 4,655,658 also describes a tool for installing captive panel fasteners. The tool is manually operated and similar to a pair of pliers. A fastener is screwed into a cartridge mounted onto one arm of the tool, and the end of the shank is deformed as the tool handles are squeezed together. The Gulistan tool is currently used for installing captive panel fasteners by major aircraft manufacturers. However, because it is hand operated using manually applied pressure, it has several drawbacks. The larger fastener diameters and thread sizes, such as ¼-28 through ⅜-24 fasteners, require more applied pressure by the artisan to flare the end of the fastener than do smaller diameter fasteners. Repetitive motion hand and forearm injuries are common and present a safety issue. Longer handles can be added to the tool to give the artisan a greater mechanical advantage, but the longer handles prevent easy access into the airframe. The greatest drawback is that the amount of pressure is not quantified and may be inappropriate to properly upset the fastener. Further, no two fasteners are flared at the same and proper upset load, because no two artisans are able to apply equal and proper pressure by hand. Artisans who use the Gulistan tool are instructed to squeeze the handles a second time to make sure the end of the fastener is properly flared. The first time the tool is squeezed, the metal at the end of the fastener is work hardened. The second squeeze then alters the hardened portion of the fastener, which can cause the fastener to malfunction or even break.
Thus, there is a need for an improved tool for installing captive panel fasteners that uses a single, controlled application of force to properly upset each fastener. There is also a need for an improved tool that provides better access to an airframe panel or work piece.